The bank, which has millions of customers, has said it is aware of the issue and is working hard to resolve them

Customers complained on Twitter that cards were rejected in shops and restaurants, while others are unable to complete payments online.

It is unclear whether customers were unable to withdraw cash from machines, with a number complaining that their cards had been blocked.

One customer said on Twitter: "Anyone else having problems with @NatWest_Help cards? Both mine and Mum cards were working an hour ago and now both being declined."

While another said: "...got declined in McDonald's how embarrassing".

@NatWest_Help my card is declined - nothing on your website, no texts to say there is an issue. I refuse to sit for 4 1/2 hour on the phone. What’s the plan? Can I get cash out of a machine? Isn’t one near me & just had to leave all my purchases on the till cuz I couldn’t pay!

The hike could push up mortgage payments by hundreds of pounds, if customers are not tied into a fixed rate deal.

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